+4°C is to the upper end of projections

if it did (which is not probable) happen it'd take until the end of the century

if we were to get there the entire world will be a different place; everything will have advanced so we won't be insuring our present world with our current knowledge and current tech but a future world with future knowledge and future tech

Sounds super optimistic. Despite some efforts to mitigate climate change. Industrialists are hell-bent on removing regulations and consuming more power than ever. Cooling things is expensive and the laws of thermodynamics don't care about how advanced a society is.

"All natural and technological processes proceed in such a way That the availability of the remaining energy decreases In all energy exchanges, if no energy enters or leaves an isolated system The entropy of that system increases Energy continuously flows from being concentrated To becoming dispersed, spread out, wasted and useless New energy cannot be created and high grade energy is being destroyed An economy based on endless growth is Unsustainable"

It's just a matter of time at that point

> if we were to get there the entire world will be a different place; everything will have advanced so we won't be insuring our present world with our current knowledge and current tech but a future world with future knowledge and future tech

That's a very convoluted way to spell "famine, wars and mass immigration". Techno-solutionism has become a religion, you don't even have to understand or look at the problem, just repeat "tech will save us all, in tech we trust".

Not everything advances. We still have houses built in the 1800s/1900s that are usable in predictable/similar climates/circumstances. A changing climate changes that.

Sure, we could bulldoze everything and build new stuff that can handle a +2C, +3C, +4C, etc... world, but that's expensive.

There are 2b+ people living in "inadequate housing", don't have sewers, don't have running water right now, we can't even fix the problem now, we're not going to fix it better when 2b more need AC to survive every summer

https://unhabitat.org/news/13-jul-2023/the-world-is-failing-...

It's not just expensive. Steel and concrete are some of the largest drivers of CO2 emissions and toxic waste, in the ballpark of 15%! So really the only sane choice is to avoid building new homes whenever possible and try to keep old houses in use as long as possible.

We're up +1.5C already and it's a polynomial growth. This current figure was also on the "upper end" of projections from 25 years ago.

> most of the time, they're optimistic.

Evidence? Has anyone collated predictions over time and compared them with outcomes to date?

I can remember a number of specific predictions (e.g. that snow would be unknown in most of the UK by the early 2000s) that were pessimistic. Of course, I recall those because they got a lot of media attention at the time and the media reporting is biased to the most extreme predictions so its not a fair sample.

HN just had a "Whoops we undercounted plant C02 absorption by 40% for the last 40 years" post so I would say the errors mostly go in one direction.

Isn't that overly pessimistic, not optimistic?

Surely if plants are absorbing more CO2 than we thought, that's a good thing for climate change? (More CO2 absorbed by plants -> less CO2 staying in the atmosphere -> less warming. No?)

I think the counting errors were "we expected these sinks to fill up slower. They are already full, and not contribute instead of being a sink".

>(More CO2 absorbed by plants -> less CO2 staying in the atmosphere -> less warming. No?)

The vast vast vast majority of co2 absorbed by plants remains in the carbon cycle. The share that leaves it is in fact ridiculously small.

There's absolutely no reasonable scenario where we wait for plants to deal with the output of the fossil fuels pumped up.

Most emitted CO2 also remains in the carbon cycle.

What matters is accumulation at a particular point in the cycle because CO₂ is added to the atmosphere faster than it is removed. If it is removed faster then it ceases to be a problem.

I'm not sure what you're trying to say here. It seems to me the first and last line don't really add anything and I don't see why the middle sentence is necessarily true.

I don't understand this reasoning. How does the presence of a single recent post on HN say anything about if the errors go in one direction or in both directions?

The errors on direct influences to warming have been overwhelming on the "too optimistic" direction. We are above the most pessimistic predictions from decades ago.

The errors on consequences of the warming... I'm not sure one can even talk about them without citing specific studies, because those things tend to have undefined timeframes and way into the future contexts (like this 4°C one... is this even possible to achieve by burning fossil fuels?)